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CSB Releases Update on U. S. Steel Clairton Coke Plant Accident
09/30/2025 - The U.S. Chemical Safety and Hazard Investigation Board (CSB) released an update on its investigation into the United States Steel Corporation Clairton coke plant accident that occurred in August.
According to a release from CSB, preliminary information indicates the explosion occurred during maintenance activities “involving a gas isolation valve in the basement of the Battery 13/14 transfer area at the facility.”
“The focus of the CSB’s investigation is understand what caused this terrible tragedy and identify actions that can be taken to prevent something like this from happening again,” said Steve Owens, a CSB chairperson.
U. S. Steel employees, assisted by MPW Industrial Services Inc. personnel, were in the process of performing a procedure to close and reopen the valve. When they attempted to flush the valve seat with water, gas monitors began alarming. Less than a minute after both a verbal and radio evacuation call was issued, an explosion occurred.
The gas isolation valve involved was a cast iron, 18-inch, double-disc gate valve. It was manufactured over 70 years ago in 1953 and had been refurbished in 2013. Examination after the incident showed the valve body had split open along a fully circumferential crack. Other valves recovered from the scene also showed signs of damage.
Two U. S. Steel employees were killed in the explosion; five other workers were seriously injured and hospitalized. Six others were treated for injuries but not hospitalized, said the CSB. The explosion also caused extensive structural damage to the Battery 13/14 transfer area and resulted in search and rescue operations.
The CSB is continuing to collect evidence and conduct analysis. It will issue a final report detailing findings, analyses and recommendations at the conclusion of its investigation.
To read the full report, click here.
“The focus of the CSB’s investigation is understand what caused this terrible tragedy and identify actions that can be taken to prevent something like this from happening again,” said Steve Owens, a CSB chairperson.
U. S. Steel employees, assisted by MPW Industrial Services Inc. personnel, were in the process of performing a procedure to close and reopen the valve. When they attempted to flush the valve seat with water, gas monitors began alarming. Less than a minute after both a verbal and radio evacuation call was issued, an explosion occurred.
The gas isolation valve involved was a cast iron, 18-inch, double-disc gate valve. It was manufactured over 70 years ago in 1953 and had been refurbished in 2013. Examination after the incident showed the valve body had split open along a fully circumferential crack. Other valves recovered from the scene also showed signs of damage.
Two U. S. Steel employees were killed in the explosion; five other workers were seriously injured and hospitalized. Six others were treated for injuries but not hospitalized, said the CSB. The explosion also caused extensive structural damage to the Battery 13/14 transfer area and resulted in search and rescue operations.
The CSB is continuing to collect evidence and conduct analysis. It will issue a final report detailing findings, analyses and recommendations at the conclusion of its investigation.
To read the full report, click here.
